Kinetics of the oxidation of N-aminopiperidine with chloramine

The kinetics of the oxidation of N-aminopiperidine with chloramine was studied at different temperatures, with variable concentrations of the two reactants and at a pH ranging between 12 and 13.5. The reaction showed to be involving two steps: the first corresponded to the formation of a diazene intermediate, the second to the evolution of this intermediate into numerous compounds within a complex reactional chain. The rate law of the first step was determined by the Ostwald method and found to be first order with respect to each reactant. The rate constant was determined at pH 12.89 and T = 255°C: k ₂ = 1.15 × 10⁵ exp(−39/RT) l mol⁻¹ s⁻¹ (E ₂ in kJ/mol). With decreasing pH value, the first exhibited acid catalysis phenomena, and diazene was converted into azopiperidine particularly faster. This created overlapping UV-absorptions between chloramine and azopiperidine, also observed in HPLC. GC/MS analyses were used to identify some of the numerous by-products formed. Their proportions are dependent of both pH and the reactants’ concentrations ratio. A reaction mechanism taking this relationship into account was suggested. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 1, pp. 112–119. The article is published in the original.